1. Field of the Invention
Embodiments of the present invention generally relate to a load cup for transferring substrates in a chemical mechanical polishing system.
2. Description of the Related Art
Chemical mechanical polishing generally removes material from a substrate through a chemical or a combined chemical and mechanical process. In a typical chemical mechanical polishing system, a substrate is held by a polishing head in a feature side down orientation above a polishing surface. The polishing head is lowered to place the substrate in contact with the polishing surface. The substrate and polishing surface are moved relative to one another in a predefined polishing motion. A polishing fluid is typically provided on the polishing surface to drive the chemical portion of the polishing activity. Some polishing fluids may include abrasives to mechanically assist in the removal of material from the substrate.
A substrate transfer mechanism, commonly referred to as a load cup, is used to transfer the substrate into the polishing head in a feature side down orientation. As the feature side of the substrate faces the load cup while the substrate is retained therein, care must be taken to avoid damage to the feature side of the substrate through contact with the load cup. For example, the feature side of the substrate may be scratched by surfaces of the load cup that support the substrate. Additionally, particulates generated during the substrate transfer or generated by contact of the substrate to the load cup may be carried on the substrate's surface to the polishing surface. During polishing, these particulates may cause substrate scratching, which results in non-uniform polishing and device defects. Therefore, it is advantageous to minimize substrate to load cup contact.
Substrate damage may also result from misalignment between the load cup and the polishing head. Typically, the load cup and the polishing head are positioned relative to each other with close tolerances to ensure trouble-free exchange. However, if the substrate is not correctly positioned within the load cup when the polishing head is lowered to retrieve the substrate, the polishing head may contact and cause damage to the substrate.
Therefore, improved load cup substrate sensing is needed to reduce damage to the substrate during substrate transfer in a chemical mechanical polishing system.